<div class="form-group">
    <select name="country" class="combobox form-control" ng-model="selected.id" my-combobox required>
        <option value="" ng-selected="!selected.id">Select a country</option>
        <option ng-repeat="country in countries" value="{{country.id}}"
                ng-selected="selected.id == country.id">{{country.name}}
        </option>
    </select>
</div>